I've been spending my time on the flight on Delta between New York and Atlanta, reading the SDK and playing around with the 4074 build of Longhorn. So far, I've noticed a couple of people peeking over my shoulder but no one has asked about it yet.
I have seen a little strangeness, for example, I can't create new folders in explorer and Longhorn doesn't recognize my USB ports anymore thus creating some frustration when trying to get to my external hard drive or to see if my TouchStream LP will work will play well with Longhorn.
Looks like the Sparkline implementation in XAML will be the first one of my Longhorn projects.